1. Field of the Invention
The present invention relates to a finishing apparatus for a printing apparatus, and more particularly to an arrangement that partially integrates the structural and functional aspects of a stacking tray and a retractable compiling shelf to provide a compact finishing apparatus.
2. Description of Related Art
The present invention is particularly suitable for receiving and fastening collated sets of copy sheets; that is, the invention is particularly suitable for, but not limited to, precollation copying, i.e., automatically plurally recirculated document set copying provided by a physical or electronic recirculating document handling system or "RDH", although the invention is also compatible with nonprecollation or post collation copying. Precollation, collation, recirculative, or RDH copying, as it is variably called, is a known desirable feature for a copier or printer. It provides a number of important known advantages. In such precollation copying any desired number of collated copy sets or books may be made by making a corresponding number of recirculations of the set of documents in collated order past the copier imaging station and copying each document page (normally only once) each time it circulates through the imaging station. The copies therefrom may exit automatically the copier processor in proper order for stacking as precollated sets, and thus do not normally require subsequent separation and collation in a sorter or collator. On-line finishing (stapling or stitching and/or gluing or other binding) and/or removal and stacking and offsetting of completed but unfinished copy sets may thus be provided while further collated copy sets are being made in further circulations of the same document set.
Examples of prior automatic on-line collating copier finishers (staplers, stitchers, gluers or other binders) and/or offsetters and their controls are referenced in U.S. Pat. No. 4,782,363 to Britt et al., the disclosure of which is incorporated herein by reference.
A discussion of references that appear pertinent to the present invention follows:
U.S. Pat. No. 4,497,478 discloses an apparatus including a housing to be positioned adjacent a copy machine to receive copies from the machine. The apparatus squares the copies, staples them together and finally stacks them.
U.S. Pat. No. 4,605,211 discloses a sheet processing device adapted to be mounted to the sheet output portion of an image-forming apparatus. The device receives output sheets, automatically aligns them to one another, and then binds them in a bundle.
U.S. Pat. No. 4,871,158 discloses a finishing apparatus for binding copy sheets received in succession at a sheet compilation station. The compilation station is defined by a movable, horizontally arranged plate upon which sheets are collected, as well as stapling heads for two or more stapling apparatus. When the last sheet of a set to be stapled is collected, the plate is quickly retracted from the set in timed sequence with the clamping of the stapling heads. Subsequently the set is dropped onto a vertically movable tray.
The above-discussed patents describe techniques for compiling sheets in a first location, and then ejecting the completed set therefrom to a separate, second set stacking location. The employment of two separate locations tends to unduly increase the size and cost of these prior art finishers. For example, in the arrangement disclosed by U.S. Pat. No. 4,871,158, the compiling tray must be retracted a distance equaling at least the width or length of the stapled set of copy sheets. Accordingly, a substantial space must be allotted in the printing apparatus to accommodate the compiling tray when it is disposed in the retracted position.
In contrast to the above-discussed patents, U.S. Pat. No. 4,424,963 discloses a compact single-tray finisher. In the arrangement disclosed by U.S. Pat. No. 4,424,963, copy sheets are directed to an accumulation device and stapling mechanism by way of a vacuum transport device. The accumulation device and stapling mechanism are disposed adjacent to a stacking/compiling tray, so that sheets clamped into the accumulation device have portions that are (apparently) draped onto an output tray. In operation, the copy sheets are transported to and securely clamped into the accumulation device until a predetermined number of sheets is accumulated therein. Once the predetermined number is achieved, a staple is driven through the stack, and the stack is released from the accumulation device and stapling mechanism, so that it falls onto the output tray.
Even though the concept underlying the design of U.S. Pat. No. 4,424,963 may be superior to the concepts underlying the designs of the above-discussed patents, the design of U.S. Pat. No. 4,424,963 is not optimum. For example, the mechanism used to feed leading edges of the copy sheets into the accumulation device and stapling mechanism, namely the vacuum transport device, would be expensive. Moreover, since the trailing edges of the collected sheets rest on the output tray or the completed stack(s), a substantial portion of the stack being compiled droops. Consequently the sheets being compiled would have a natural tendency to pull away from the accumulation device and out of registration.
Other important examples of references that disclose finishers using at least a portion of one tray to both compile and stack completed sets of copy sheets include a European Patent Application having the Publication No. 346,851 A1, and an operator's manual for the AutoStapler II--the AutoStapler II being a finisher used in Canon Copiers NP4835, NP6650, and NP8580. The finisher of the European Patent Application includes an accommodation tray, i.e. a stacking tray, positioned adjacent to a fixed stacking portion, i.e. a compiling shelf, the compiling shelf having front and rearward portions. A vertical abutment plate (end stop) is movably disposed on the fixed compiling shelf, while rollers, through which copy sheets are ejected, are positioned intermediate of the front and rearward portions of the compiling shelf. A stapler is positioned near the rearward portion of the compiling shelf. The stacking tray is underlain by an elevator, while a positioning plate or tamper is positioned along a lateral edge of the stacking tray. In operation, the abutment plate is positioned on the rearward portion of the compiling shelf and copy sheets are ejected through the rollers such that a set of the sheets is collected in both the stacking tray and the compiling shelf. Edges of the sheets are aligned or registered by the tamper and the abutment plate. Once a set has been collected and registered, a staple is driven through a corner thereof, and the stapled set is ejected from the compiling shelf by use of the abutment plate, so that the set either rests on the surface of the stacking tray or another stapled set of copy sheets. The finisher of said European Patent Application represents an improvement over the finishers of the above-discussed patents in that it does not require that the entire width or length of the stapled set be ejected from the compiling shelf. Since stapled sets are ejected by moving the abutment plate across the entire length of the compiling shelf, however, ejection distance is not optimally minimized. Indeed, it is desirable to minimize ejection distance as much as possible to not only control the speed at which the finisher is capable of operating, but to insure that the stapled sets are not scattered as a result of being pushed an excessive distance.
Conceptually, the AutoStapler II is structurally similar to and operates in much the same way as the finisher of the European Patent Application. However, it uses a closing nip of ejection rollers for set ejection. Both of these finishers employ a mechanism for controlling stack height of stapled sets that collect on the stacking tray. The mechanism of the AutoStapler II includes a pivotable lever having a first end disposed in front of the compiling shelf and a second end in contact with a sensor disposed above the compiling shelf. In operation, the lever rests on the stacking tray or the stack of collected sets. Each time the stack changes, on account of a set being ejected from the compiling shelf, the lever is pivoted so that it contacts the sensor and moves the elevator, and hence the stacking tray, down by a predetermined distance.
While the stack height control mechanism of the AutoStapler II represents an advance in the art, it could pose problems to the unwary user. In particular, since the lever is disposed on top of the stack of stapled sets it must be pivoted each time the user removes the stack from the stacking tray. Inadvertently the unwary user could cause the sensor to be actuated, thus causing undesirable movement of the elevator. The exposed level could even be damaged by a careless operator. For a general discussion of stack sensors, reference is made to U.S. Pat. No. 4,469,320 and prior art cited therein.
In view of the discussion above, it would be desirable to provide a compact finishing apparatus that optimally minimizes ejection distance of stapled sets from a compiling shelf to a stacking tray. Moreover, it would be desirable if the height of the stacking tray could be varied by an elevator through use of a sensing mechanism that is disposed remotely with respect to the stacking tray and/or stapled sets of copy sheets deposited thereon.